Crystal structure and thermoelectric properties of the type-I clathrate compound Ba₈Ge₄₃ with an ordered arrangement of Ge vacancies

The crystal structure of the type-I clathrate compound Ba₈Ge₄₃ has been investigated by x-ray diffraction and transmission electron microscopy. The thermoelectric properties of Ba₈Ge₄₃ have also been investigated. The crystal structure of Ba₈Ge₄₃ is different from that reported for the usual type-I clathrate compounds with the space group of Pm3n but is a superlattice structure based on the usual type-I clathrate structure due to the ordering of Ge vacancies in half the 6c sites of the usual type-I clathrate structure. The crystal structure of Ba₈Ge₄₃ belongs to the space group of Ia3d and Ge vacancies exclusively occupy the 24c sites. The thermoelectric properties of Ba₈Ge₄₃ are not particularly good, as exemplified by the rather low ZT value of 0.057 because of the high value of electrical resistivity, which may arise from the existence of Ge vacancies.